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Is your feature request related to a problem? Please describe.
Currently, the metadata service assumes it can connect to elasticsearch over plain http with no authentication.
This seems distinctly less than ideal and doesn't suit our possible deployment.

Describe the solution you'd like
To be able to supply parameters in the helm chart which ultimately allow setting any of the parameters available for Elasticsearch() (see https://elasticsearch-py.readthedocs.io/en/latest/api/elasticsearch.html).
At the very least, I would need to be able to set the scheme, api_key and verify_certs parameters.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

While it would be fairly straightforward for me to just add the parameters I need at the various places they get passed around, it would seem sensible to do something more general that allows passing arbitrary parameters to Elasticsearch() (which would hopefully also mean that if new parameters were added, the code here wouldn't have to change to take advantage of them). But that would probably be a breaking change, or at the very least require code to recognize the current configuration options and map them into the new ones.